The proposed research is planned to investigate, in an animal model, the effects of active and passive vasomotion of coronary stenoses on flow and resistance in the stenotic coronary artery. We have data showing that the resistance of a noncircumferential coronary stenosis changes in response to various interventions suggesting, therefore, that these stenoses may passively change in caliber and thus affect flow. Such passive changes may cause myocardial ischemia. We plan to study changes in flow and resistance in different types of coronary stenoses in response to vasoactive drugs and physiologic interventions in open chest dogs. Studies of stenosis caliber using ultrasonic dimension transducers are also planned. Studies of the effects of exercise on the hemodynamics of coronary stenoses are planned in intact awake dogs. The proposed work is planned to help develop an understanding of the potential mechanisms by which a severe coronary stenosis may lead to myocardial ischemia or infarction.